The present invention relates to a method for producing a container whose interior is substantially under atmospheric pressure, by means of a vacuum welding process.
In a number of applications, it is necessary for a container which is hermetically sealed under vacuum to have substantially atmospheric pressure in its interior because devices or objects disposed therein must remain subjected to such a defined pressure of a given gas or gas mixture.
In particular, containers in the form of housings for implantable cardiac pacemakers must be tightly and hermetically sealed so that aggressive body fluids cannot reach the interior. If body fluids penetrated into the interior, they would cause irreversible damage in the components which may result in malfunction of the pacemaker. In order to attain a high sealing effect with high resistance to the attack of body fluids, a cobalt alloy is used for the housing which is sealed under vacuum by means of electron beam welding.
In order to be able to operate, certain types of primary elements used to supply the electronic circuit of the pacemaker with current require ambient pressure in the order of magnitude of atmospheric pressure. In some types of pacemakers, the gas with which the interior of the housing is filled under atmospheric pressure is helium.
In order to prevent the gas used to fill the interior from flowing out, it is necessary to seal the housing. This is accomplished in many cases by first welding the housing wall components together under vacuum while leaving an opening, removing the vacuum and then filling the interior of the housing through the opening with gas under atmospheric pressure, and thereafter soldering the opening under pressure conditions which correspond to those in the housing interior. Instead of soldering, the remaining opening can be closed by casting with plastic or by resistance welding in a similar manner.
This process has the drawback that the housing is not sealed completely hermetically by a uniform welding process. The advantages of a weld connection produced by means of an electron beam under vacuum cannot become effective, for example, unless all housing openings are welded shut according to this method, since the total properties of the container and its usefulness are significantly reduced by but a single weak point.